Friction materials

ABSTRACT

A friction material for friction braking or transmission systems including in its finished state a two-part binder system, one part being a phenolic thermosetting resin and the other part being uncombined nickel and sulphur. The nickel and sulphur are capable of reacting together under the action of heat generated during application of the system to form nickel sulphide which provides additional binding in the material and compensates for thermal decomposition of the resin. Friction modifiers and fillers may also be included.

United States Patent 91 Lumb et al. 51 Mar. 27, 1973 [54] FRICTIONMATERIALS References Cited [75] Inventors: John B. Lumb, Bradford;Michael UNITED STATES PATENTS Edwards Leeds both of England 2,252,9918/1941 Steck ..L.260/DIG. s9 [73] Assignee: BBA Group Limited,Cleckheaton, 3,231 2,11

Yorkshire, England 3,492,262 1970 [22] Filed: Apr. 13, 1971 r PrimaryExaminer-Lewis T. Jacobs [2]] Appl' 133765 Attorney-Stevens, Davis,Miller & Mosher 57 ABSTRACT [30] Foreign Application Priority Data Afriction material for friction braking or transmission p 1970 GreatBritain systems including in its finished state a two-part binder Sept.30, 1970 Great Britain ..46,434/70 system, one part being a phenolicthermosetting resin v and the other part being uncombined nickel and v Jsulphur. The nickel and sulphur are capable of react- [52] US. Cl...;.260 /38, 260/DIG. 39 ing together under the action f heat generatedduring [51] Int. Cl. ..C08g 51/04, C08g 51/10 application of the systemto form nickel sulphide [58] Field of Search .260/38, 39 M, DIG. 39;106/36; which provides additional binding in'the material andcompensates for thermal decomposition of the resin.

Friction modifiers and fillers may also be included.

8 Claims, No Drawings FRICTION MATERIALS This invention relates tofriction materials of the kind (hereinafter referred to as thekindspecified") which are particularly intended for use in providingcontact surfaces in friction braking or transmission systems suchforexample as used in disc brakes, internal shoe drum brakes, clutchfacing, and railway brake blocks.

. Hitherto such friction 'materials have usually consisted of mixturesof fibrous material, generally fibrous inorganic material, such asasbestos fiber, metallic and non-metallic fillers, binders, and frictionmodifiers, the mixture being-moulded into a dense state by theapplication of heat and pressure.

Friction materials which are to be used in disc brakes are subjected toconsiderably higher temperatures and pressures than the material whichis intended for use in drum brake installations, and consequently havehigher rates of wear. Moreover, the higher temperatures can also lead toa thermal breakdown of the binder material, which causes the coefficientof friction of the material to decrease. The reduction in thecoefficient of friction of the material, which sometimes occurs duringheavy and continuous braking, is referred to as fade.

According to the present invention there is provided a friction breakingor transmission system having a friction material of the kind specifiedfor effecting braking or for transmitting power in which the frictionmaterial comprises a two-part binder system, one part comprising athermosetting resin and the other part comprising a mixture of at leasttwo materials which combine progressively under the action of heatdeveloped as a result of frictional engagement of the friction materialwithin the braking or transmission system to provide additional bindingfor the friction material.

Suitable materials which combine progressively under the action ofsuch-heat are nickel and sulphur.

According to another aspect of the invention therefore, there isprovided a compacted friction material of the kind specified comprisingfinely divided nickel, sulphur and a binder comprising a thermosettingresin.

The invention further provides a compacted friction material of the kindspecified including a binder which comprises a thermosetting resin part,and a further part which consists of nickel sulphide formed in situ fromI finely divided nickel and powdered sulphur.

This invention also includes a method of manufacturing a frictionmaterial comprising the steps of mixing together fibrous material, suchas asbestos, finely divided nickel, sulphur and a thermosetting resin,compressing the mixture and heating the compressed mixture to atemperature sufficiently high to cure the thermosetting resin. I

In one method in accordance with the invention the mixture is heated toa temperature sufficiently high to cure the thermosetting resin and tocause at least some of the finely divided nickel to combine with atleast some of the sulphur to form nickel sulphide.

The thermosetting resins which may be incorporated in a frictionmaterial according to the invention may be an organic thermosettingresin, such as phenol formaldehyde, or an organic thermosetting resinwhich has been modified by the substitution of inorganic groups on tothe organic molecule e.g. borated phenolic resins. Mixtures of differentthermosetting resins of either type may also be used in a frictionmaterial according to the present invention.

The friction material may also contain a filler, which may be a metallicinclusion, such as brass powder, or a non-metallic filler, such ascalcium carbonate powder, rottenstone or any other filler well-known inthe art. Friction modifiers may also be incorporated in the frictionmaterial. These materials help to maintain the coefficient of frictionat the desired level over varying temperature ranges. Thus, it may benecessary to in crease the coefficient of friction, in which caseabrasive friction modifiers such as alumina and/or carborundum powdercan be incorporated in the material. On the other hand, if it is desiredto reduce the coefficient of friction of the material, lubricativefriction modifiers such as graphite or barytes (barium sulphate) may beadded.

Our investigations have suggested that, in friction materials whichincorporate only conventional thermosetting resin binders, the heatgenerated under heavy and prolonged braking is often sufficient todecompose the thermosetting resin on the contacting surfaces of thefriction material, and this results in fade and high rates of wear. Ourinvention is based upon the development of a friction material for usein friction braking or transmission systems which friction materialcontains materials such as nickel and sulphur,which can react with eachother under the action of heat developed as a result of thefrictionalengagement of the friction material within the system. The materials,when reacted, provide additional binding for the friction material andcompensate for any deterioration in friction or wear characteristics ofthe friction material as a result of thermal decomposition of thethermosetting resin.

We have found that finely-divided nickel and sulphur are particularlysuitable materials for incorporation in friction materials. Thesesubstances react together to form nickel sulphide when heated (to atemperature such as is developed in friction braking or transmissionsystems as a'result of prolonged application of the system. When thematerials are incorporated in a friction material,the nickel sulphidegenerated by reaction of the nickel and sulphur forms a matrix whichbinds together the friction material and thereby prevents furtherdeterioration of the friction material.

Friction materials incorporating nickel and sulphur may be manufacturedby mixing finely divided nickel and sulphur, asbestos, or otherinorganic fibrous material with a thermosetting resin, compressing themixture, and heating the compressed mixture to a temperaturesufficiently high to cure the resin e.g. between and C. Preferably, theheating is carried out in two stages, first by applyingsufficient heatpartly to cure the thermosetting resin whilst-compressing the mixture,and subsequently heating the mixture after compression in order tocomplete the curing of the resin. After curing at these temperatures,the finished friction material will contain litter or no nickelsulphide. However, nickel sulphide will be formed from the nickel andthe sulphur under the action of heat developed as a result of thefrictional engagement of the friction material within the frictionbraking or transmission system.

An alternative manufacturing process, however, is to cure the compressedmixture at sufficiently high temperatures to effect reaction of thenickel and the sulphur, e.g. at temperatures in excess of 250 C., and

preferably in the region of 300 C. in this case, the nickel and sulphurin the finished friction material will be wholly or substantially whollypresent as nickel sulphide, and no further reaction will take place inthe friction material when it is used.

In a preferred method of forming friction material according to thepresent invention inorganic fibrous material, fillers, thermosettingresin, finely divided nickel, sulphur and any desired friction modifiersare all intimately mixed together in a mixer or blending machine. Amoulding operation is then carried out in which a mould, for example, adisc pad mould, is charged with the mixture. The mixture is then curedby the application of heat and pressure. Generally the curing time is inthe order of five to ten minutes and the pressures which are applied tothe mould are from onehalf to 10 tons per square inch. It will beappreciated that the precise temperatures and pressures used in themoulding operation depend upon the relative quantities of theconstituents of the friction material.

The initial application of heat and pressure causes the mixture partlyto cure. The composition of the partly cured mixture depends upon thetemperature and the length of time for which the mixture was cured.Thus, the temperature and curing period in the moulding operation mayonly be sufficiently high to initiate curing of the thermosetting resin.For example, the temperature on the face of the mould may be between 120and 180 C. Alternatively, if higher temperatures are used, for examplein excess of 250 C., combination of the finely divided nickel with thesulphur to form nickel sulphide may be initiated. The partly-curedmixture is then removed from the mould and heated in an ovensufficiently to complete the curing process. For example, thepartly-cured mixture may be heated for 2 to 24 hours at a temperature offrom 90 to 300 C. Depending on the temperature selected, the finishedproduct will contain completely cured thermosetting resin, the nickeland sulphur being either uncombined or partly or completely combined asnickel sulphide.

An example of the ingredients (in parts by weight) from which frictionmaterial according to the present invention may be made is shown below:

An example of friction material made according to the present inventionis shown below:

Ingredient Parts by Weight Asbestos fiber 25 Phenolic resin 8 Nickel l5Sulphur 6 Brass powder 10 Graphite 6 Barytes 24 The ingredients wereweighted out and mixed together in a blending machine for 30 minutes.The materials were then charged into a disc brake pad mould, and mouldedin a press at a temperature of 155 C. and at a pressure of 1 ton persquare inch for 10 minutes. The material was then removed from themould, placed in an oven and heated at a temperature of 180 C. for 10hours.

The nickel and sulphur contained in the finished material were mainlypresent as the uncombined elements.

The materials were tested on an inertia dynamometer in order toinvestigate their wear characteristics as follows:

Two pads of the friction material each having an area of 5 square incheswere used as brake pads in an automobile disc brake caliper, each padbeing located on a respective side ofa 10 inch diameter braking disc.

The material was subjected to a test schedule of 150 applications'inwhich the rate of rotation of the disc was equivalent to road speeds ofup to mph. Under these conditions kinetic energy of up to 40 X 10 ft lbfwas dissipated. During part of the test torque was maintained at 400 lbfft and during the remainder it varied between and 600 lbf ft. Thetemperature measured on the face of the braking disc during the testschedule varied from ambient to 400 C. The average wear on each of thedisc pads after the test schedule was 0.005 inches.

A conventional friction material based on asbestos and a thermosettingresin was subjected to an identical test schedule and the average wearon each of these disc pads was 0.030 inches.

We claim:

1. A compacted wear-resistant friction material for use in frictionbraking or transmission systems, the said friction material in itsfinished state comprising from 10 50 by weight of inorganic fibrousmaterial in a two-part binder system, one part of said binder comprising5 to 30 parts by weight of a phenolic thermosetting resin, and the otherpart of said binder comprising a mixture of 2 to 30 parts by weight offinely divided nickel and 2 to 15 parts by weight of powdered sulphur,the nickel and sulphur capable of progressively combining under theaction of heat developed as a result of the frictional engagement of thefriction material within the braking or transmission system to provideadditional binding in the friction material.

2. A compacted wear-resistant friction material for use in frictionbraking or transmission systems, the said friction material in itsfinished state comprising from 10 to 50 parts by weight of an inorganicfibrous material,

five to 30 parts by weight of phenolic thermosetting.

resin, two to 30 parts byweight of finely divided nickel and two to 15parts by weight of powdered sulphur, substantially all of the nickel andthe sulphur being uncombined, the uncombined nickel and sulphur capableof progressively combining with each other under the action of heatdeveloped as a result of frictional engagement in the system to provideadditional binding in the friction material.

3. A compacted wear-resistant friction material for use in frictionbraking or transmission systems, the said friction material in itsfinished state comprising from 10 50 parts by weight of an inorganicfibrous material, five to 30 parts by weight of phenolic thermosettingresin, two to 30 parts by weight of finely divided nickel and two toparts be weight of powdered sulphur, a portion of the nickel and sulphurbeing combined in situ as nickel sulphide, and another portion of thenickel and sulphur being uncombined and capable of progressivedehyde.

8. ln a method wherein a friction material pad is engaged with a movingelement of a friction braking or transmission systems which producesheat by friction,

the improvement comprising: maintaining the frictional qualities of saidfriction material pad by utilizing a wear-resistant frictional materialwhich comprises 10 to 50 parts by weight of inorganic fibrous materialin a two-part binder system, one part of said binder comprising five to30 parts by weight of a phenolic thermosetting resin, and the other partof said binder comprising a mixture of two to 30 parts by weight offinely divided nickel and two to 15 parts by weight of powdered sulphur,wherein at least a portion of said nickel and said sulphur areuncombined, whereby the frictional heat produced progressively combinesthe uncombined nickel and sulphur to produce additional binding in thefrictional material during use.

2. A compacted wear-resistant friction material for use in frictionbraking or transmission systems, the said friction material in itsfinished state comprising from 10 to 50 parts by weight of an inorganicfibrous material, five to 30 parts by weight of phenolic thermosettingresin, two to 30 parts by weight of finely divided nickel and two to 15parts by weight of powdered sulphur, substantially all of the nickel andthe sulphur being uncombined, the uncombined nickel and sulphur capableof progressively combining with each other under the action of heatdeveloped as a result of frictional engagement in the system to provideadditional binding in the friction material.
 3. A compactedwear-resistant friction material for use in friction braking ortransmission systems, the said friction material in its finished statecomprising from 10 50 parts by weight of an inorganic fibrous material,five to 30 parts by weight of phenolic thermosetting resin, two to 30parts by weight of finely divided nickel and two to 15 parts be weightof powdered sulphur, a portion of the nickel and sulphur being combinedin situ as nickel sulphide, and another portion of the nickel andsulphur being uncombined and capable of progressively combining witheach other under the action of heat developed as a result of frictionalengagement in the said system to provide additional binding in thefriction material.
 4. A material according to claim 2, containing 5 to20 parts by weight of nickel.
 5. A material according to claim 2 furtherincluding a friction modifier.
 6. A material according to claim 2further including a filler.
 7. A material according to claim 2 whereinthe phenolic thermosetting resin comprises at least one compoundselected from the group consisting of phenol formaldehyde and boratedphenol formaldehyde.
 8. In a method wherein a friction material pad isengaged with a moving element of a friction braking or transmissionsystems which produces heat by friction, the improvement comprising:maintaining the frictional qualities of said friction material pad byutilizing a wear-resistant frictional material which comprises 10 to 50parts by weight of inorganic fibrous material in a two-part bindersystem, one part of said binder comprisinG five to 30 parts by weight ofa phenolic thermosetting resin, and the other part of said bindercomprising a mixture of two to 30 parts by weight of finely dividednickel and two to 15 parts by weight of powdered sulphur, wherein atleast a portion of said nickel and said sulphur are uncombined, wherebythe frictional heat produced progressively combines the uncombinednickel and sulphur to produce additional binding in the frictionalmaterial during use.